21056 has 28 divisors (see below), whose sum is σ = 48768. Its totient is φ = 8832.

The previous prime is 21031. The next prime is 21059. The reversal of 21056 is 65012.

21056 is nontrivially palindromic in base 13.

It is a tau number, because it is divible by the number of its divisors (28).

It is a Harshad number since it is a multiple of its sum of digits (14).

It is an alternating number because its digits alternate between even and odd.

It is a nialpdrome in base 8.

It is a self number, because there is not a number n which added to its sum of digits gives 21056.

It is not an unprimeable number, because it can be changed into a prime (21059) by changing a digit.

21056 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 425 + ... + 471.

2²¹⁰⁵⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21056, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24384).

21056 is an abundant number, since it is smaller than the sum of its proper divisors (27712).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21056 is an equidigital number, since it uses as much as digits as its factorization.

21056 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66 (or 56 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21056 is about 145.1068571777. The cubic root of 21056 is about 27.6137437676.

Adding to 21056 its reverse (65012), we get a palindrome (86068).

Subtracting 21056 from its reverse (65012), we obtain a triangular number (43956 = T₂₉₆).

It can be divided in two parts, 2 and 1056, that multiplied together give a palindrome (2112).

The spelling of 21056 in words is "twenty-one thousand, fifty-six".